<template>
  <div class="vm">
    <h2 class="h-title">聚合数据</h2>
    <div id="map" class="map-x"></div>
  </div>
</template>

<script>
import 'ol/ol.css'
import { Map, View } from 'ol'
import Tile from 'ol/layer/Tile'
import OSM from 'ol/source/OSM'
import { Style, Circle, Stroke, Fill, Text } from 'ol/style'
import layerVector from 'ol/layer/Vector'
import sourceVector from 'ol/source/Vector'
import Cluster from 'ol/source/Cluster'
import Point from 'ol/geom/Point'
import Feature from 'ol/Feature'

export default {
  name: 'Polymerization',
  data () {
    return {
      map: null
    }
  },
  methods: {
    initMap () {

      let count = 20000 // 点的数量
      let features = [] // 存放点要素的数组
    
      // 初始化每个点的坐标位置
      let e = 4500000
      for (let i = 0; i < count; ++i) {
        let coordinates = [2 * e * Math.random() - e, 2* e * Math.random() - e]
        // 根据坐标生成点状几何
        features[i] = new Feature(new Point(coordinates))
      }

      // 把点状要素放到矢量源里
      let source = new sourceVector({
        features
      })

      let clusterSource = new Cluster({
        // 通过 distance 来控制两个点聚合的间距，如果2个点的间距小于 distance 所设置的数时，就会以聚合的方式显示
        distance: parseInt(40, 10),
        source // 就是前面用到的矢量数据源
      })
      
      // 点的样式
      let styleCache = {}
      let clusters = new layerVector({
        source: clusterSource, // 源，指向上面的聚合数据源
        style: feature => { // feature 是聚合后的数据，每一个 feature 代表距离小于上面设置的点状要素
          let size = feature.get('features').length // features 是点状要素
          let style = styleCache[size]
          
          if (!style) {
            style = new Style({
              image: new Circle({
                radius: 10,
                stroke: new Stroke({
                  color: '#fff'
                }),
                fill: new Fill({
                  color: '#3399cc'
                })
              }),
              text: new Text({
                text: size.toString(), // 以聚合点的数量作为显示的内容
                fill: new Fill({
                  color: '#fff'
                })
              })
            })

            styleCache[size] = style
          }

          return style
        }
      })

      // 声明底图
      let raster = new Tile({
        source: new OSM()
      })

      this.map = new Map({
        target: "map",
        layers: [raster, clusters],
        view: new View({
          center: [0, 0],
          zoom: 2
        })
      })
    }
  },
  mounted () {
    this.initMap()
  }
}
</script>

<style>

</style>